The present invention relates generally to tape cassettes and, more particularly, to the construction and manufacture of a guard panel or lid forming a component of a video or audio tape cassette or cartridge which serves to selectively open and close an access opening provided in the cassette through which a magnetic head is inserted from the outside into the tape cassette.
Generally, a video or audio tape cassette is provided with a guard panel 18 (FIG. 1) which selectively opens and closes an access opening of the cassette through which a magnetic head is inserted during operation. During non-use of the tape cassette, the guard panel 18 is positioned to close the opening of the tape cassette to prevent the entry of dust carried in the air into the tape cassette. The guard panel also serves to prevent the operator from inadvertently touching the magnetic tape housed within the cassette during handling. Thus, the magnetic tape is protected from damage and contamination by the guard panel. If the magnetic tape is damaged or contaminated, a signal error may occur which will cause distortion of the displayed picture image in the case of video tape or interruption or distortion of reproduced sounds in the case of audio tape.
A tape cassette generally comprises a multi-part housing in which magnetic tape and other components are housed. Referring to FIG. 1, the housing comprises an upper half 10 and a lower half 16. Windows 14 through which the tape (not shown) can be viewed are provided in the upper half 10.
The guard panel 18 is pivotally mounted on the upper half 10 of the housing so that during non-use of the tape cassette, the guard panel 18 closes the access opening of the tape cassette as seen in FIG. 1. When the tape cassette is played, e.g., when the cassette is inserted into a tape deck (not shown) for operation, the guard panel 18 is unlocked and pivoted to an open position to provide access for the magnetic head to engage the tape within the cassette.
As seen in FIGS. 2(A)-2(D), 3 and 5, a conventional guard panel 18 comprises a narrow front plate portion 20 and a narrow upper plate portion 22. The plate portions 20 and 22 are joined to each other along respective longer sides thereof to form an integral elongated plate member having a substantially L-shaped transverse cross section. The plate member further comprises side plate portions 24a and 24b having respective projecting portions 26a and 26b, best seen in FIGS. 2A, 2C and 2D. Stub shafts 28a and 28b extend inwardly from projecting portions 26a and 26b which serve to pivotally mount the guard panel 18 to the upper half 10 of the housing. The stub shafts 28a and 28b are inserted into corresponding insertion holes (not shown) formed in the side walls near the front corner portions of the upper half 10 of the cassette housing.
As seen in FIGS. 2A and 2B, a recess 30 is formed on the surface of a central region of the elongated plate member at which the front plate portion 20 and upper plate portion 22 are joined to each other. Where the guard panel 18 is formed by means of injection molding, a molten plastic material is injected into a divisible mold provided with a cavity block and a core block through a gate formed in the cavity block. The recess 30 of the molded guard panel results from the presence of the gate in the mold.
Another recess 32 is formed in the central region of the back surface of the upper plate portion 22. In this connection the core block of the mold is provided with a protrusion which contacts the molten plastic material during the injection molding operation of guard panel 18 and results in the formation of the recess 32. It should be noted that this protrusion permits the molten plastic material which is injected into the mold to flow smoothly within the mold to provide the molded guard panel 18.
Referring to FIG. 4, a mold used for manufacturing the guard panel 18 is illustrated. The mold comprises a movable platen 34, a fixed platen 36, mounting plates 38a and 38b affixed to platens 34 and 36 respectively, back plates 40a and 40b of the mounting plates, a core plate 42, a cavity plate 44, a core block 46, a cavity block 48, a gate 52, spacer blocks 54a and 54b, an ejector plate 56 and ejector pins 58. The molded article, i.e., the guard panel, is designated 50 in FIG. 4. As is apparent from FIG. 4, molten plastic material is injected through the gate 52 to fill the space defined between the core block 46 and the cavity block 48 to form the molded article 50. When the mold is opened to remove the molded article 50, the core block 46 is moved in a direction opposite to the direction in which the cavity block 48 is moved, with the molded article 50 tightly adhering to the core block 46. At the same time, the ejector plate 56 is moved toward the cavity block 48 causing the molded article 50 to be pushed from the core block 46 by the ejector pins 58 which are affixed to the ejector plate 56. In this manner, the molded article 50, i.e., the guard panel, is removed from the core block 46.
In general, the mold is constructed to facilitate the release of the molded article 50 therefrom. Thus, the molded article 50 is readily released from the core block 46 by the pushing force of the ejector pins 58 as described above. Thus, during the injection molding operation, the back surface of the upper plate portion 22 is pushed at several points. Moreover, it should be noted that the stub shafts 28a and 28b which project inwardly from the side plate portions 24a and 24b of the guard panel 18 respectively, are readily released from the mold by a conventional mechanism (not shown) of the mold when the ejector pins 58 are pushed toward the cavity block 48.
It should be noted, however, that the front plate portion 20 and the upper plate portion 22 of guard panel 18 are joined to each other such that their longer sides intersect each other at substantially right angles. It therefore follows that the cavity block 48 must also provide a substantially right angle bend at the region at which the front and upper plate portions 20 and 22 are joined to each other. It is important to note, however, that only a slight withdrawing draft is present in the bend portion of the cavity block 48. Additionally, it is desired that the exposed or upper surface of the upper plate portion 22 be quite smooth and lustrous which requires that the surface of the molded article which will constitute the exposed surface of the upper plate portion 22 be in particularly tight contact with the cavity block 48.
If the mold is opened under these conditions, the molded article 50 is pulled with the surface of the molded upper plate portion 22 attached to the cavity block 48. As a result, the lustrous surface of the upper plate portion 22 is often deformed and cracks frequently occur, particularly at the regions near the side plate portions 24a and 24b, resulting in an unsatisfactory appearance and low mechanical strength of the guard panel.
FIG. 5 illustrates in exaggerated form the manner in which the guard panel is deformed and cracked as it is released from the mold. Specifically, the guard panel is cracked at the edge regions designated 60a and 60b. As seen in FIG. 5, the upper plate portion 22 is not substantially deformed at its central region but is deformed at regions lateral of the central region. As noted above, a protrusion (not shown) formed in the core block 46 is engaged by the molten plastic material during the molding operation to form the recess 32 at the central region of the back surface of the upper plate portion 22. The core block 46 strongly adheres to the central region of the upper plate portion 22 while the other regions of the upper plate portion 22 strongly adhere to the cavity block 48. It is therefore seen that the molded upper plate portion 22 will be deformed as it is removed from the mold in the manner shown in FIG. 5.